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Jess Nervous > Special Senses: The Eye > Flashcards

Special Senses: The Eye Flashcards

1
Q

What % of blindness is “preventable”? Name four common causes of blindness

A

50% is preventable.

ARMD (age related macular degeneration), glaucoma, cataracts, diabetic retinopathy

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2
Q

In which age groups is blindness more common?

A

1/5 >75 and 1/2 >90

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3
Q

What is phototransduction? How is it done in the eye and the ear?

A

The process in which light energy is translated into electrical energy
Eye: Light energy into electrical signals
Ear: sound energy/vibration into electrical signals

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4
Q

What is the role of photoreceptors? List the two types

A

They code the image formed on the retina into APs

Rods and Cones

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5
Q

Which component of photoreceptors are sensitive to low level light (night vision)? Where are they located?

A

Rods, located in all areas of the retina except the fovea

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6
Q

Which component of photoreceptors is responsible for daytime vision? Where is it located?

A

Cones, highest density at the fovea

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7
Q

Which component of photoreceptors can detect 3 different photopigments and which pigments can it detect?

A

Cones, can detect photopigments red, green and blue

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8
Q

What are the clinical terms for near and farsightedness?

A

Near: myopia
Far: hypermetropia

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9
Q

What process summarizes how images are focused onto the retina?

A

Refraction

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10
Q

What causes hypermetropia? Where is the image formed?

A

The lens is too weak (too flat or the eyeball is too short so that the focus lies behind the retina which is where the image forms

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11
Q

What causes myopia? Where is the image formed?

A

The strength of the lens system is too strong (too curved) or the axial length of the eye is too long so that the focus lies in front the retina which is where the image forms

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12
Q

Name five components of a vision assessment and the tools that might be used to test them + two more things that can be tested for bonus!

A
  1. Visual Acuity: snellen chart
  2. Colour vision: ishihara test
  3. Pupillary reflexes
  4. Blind spot
  5. Ophthalmoscopy/Fundoscopy

+Visual fields and eye movements

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13
Q

Define a blindspot, which area of the eye does it correspond with?

A

A small area lateral to the centre of the visual field where there is no visual perception, corresponds to the optic disc as there are no photoreceptors there

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14
Q

What does ophthalmoscopy/fundoscopy allow for the visualization of? What should you do to allow for a better ophthalmoscope examination?

A 
Should use papillary dilatation to get a better view 
Black blobs in the vitreous 
Retina
Optic nerve 
Fovea
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15
Q

What is the presence of vitreous indicative of?

A

Vitreous hemorrhage

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16
Q

What would indicate a papilloedema on a fundoscopy?

A

Swelling of the optic nerve

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17
Q

What is vitreous and where is it? What happens to it with age?

A

Gel-like substance that helps the eye maintain its round shape and becomes thinner with age. It’s in the posterior segment of the eye

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18
Q

What might you examine for when looking at the retina?

A

Hemorrhage, detachment and vessels

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19
Q

Which region of the eye has the highest density of photoreceptors in the retina?

A

The fovea

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20
Q

Describe the process of ‘accommodation’

*including the three ‘processes’ involved

A

As an object approaches, the eye light rays from it increasingly diverge, the focal point is moved backwards and the eye must accommodate with pupil constriction in order to maintain a clear image on the retina

  1. Constriction of pupils
  2. Thickening of lens (increasing its convexity) due to constriction of ciliary muscles
  3. Convergence of both eyeballs
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21
Q

What is presbyopia and which process becomes compromised in this ‘condition’?

A

Age related farsightedness as the lens becomes stiffer with age (too concave with the loss of elasticity) and there is a resulting decrease in accommodation/focusing

So close objects are no longer focused onto the retina

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22
Q

How is presbyopia corrected for?

A

Convex lens of increasing strength

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23
Q

Which muscle is responsible for changing the shape of the lens (and thus influences how much light comes into the eye?)

A

Ciliary Muscle

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24
Q

Which structure in the eye dictates the size (big or small) of the pupil?

A

The iris (as they contain circular muscles around the pupil)

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25
Q

Describe the process of the light reflex if light is shined on the LEFT eye

A
  1. Light is received from the left retina
  2. Transmitted via optic N to the pretectal nucleus (and lateral geniculate body to go down the optic tract to the occipital lobe)
  3. There is bilateral innervation from pretectal nucleus to edinger westphal nucleus
  4. Oculomotor nerve to the ciliary ganglion
  5. Short ciliary nerve transmits info from ciliary ganglion to circular muscles of the iris = pupil constriction
26
Q

What happens to the eye’s light reflex when light is shined into the left eye if there is a lesion to the L optic nerve?

A

Absent light reflex: Left and right side doesn’t constrict (no consensual constriction)

27
Q

What happens to the eye’s light reflex when light is shined into the left eye if there is damage to the optic chiasma?

A

Light reflex still present as the optic nerve can still transmit info to the midbrain/working left and right nuclei of edinger westphal (so info still gets sent to the ciliary ganglion and the circular muscles of the iris)

28
Q

What happens when light is shined into the left eye if there is damage to the L oculomotor nerve?

Therefore, what will happen if there is damage to the R oculomotor nerve when light is shined into the L eye?

A

Damage to L oculomotor nerve: Direct light reflex is absent but consensual one is present, as info is still received by the midbrain BUT the output specific to the left side is damaged

Damage to R oculomotor nerve: Direct light reflex present but consensual one is absent

29
Q

What is the direct cause of cataracts and its result on quality of vision?

A

Opacification of the lens or its capsule which changes the transparency and the refractory index of the lens - resulting in blurry or cloudy vision

30
Q

What are five associated risk-factors/causes of cataracts, when is cataracts worse?

A

Age, congenital, drugs, trauma or metabolic disturbances (i.e diabetes)
Worse in low level light (i.e driving at dusk)

31
Q

What is glaucoma?

A

A group of eye diseases that cause damage to the optic nerve (due to increased pressure in the eye)

32
Q

What is the aetiology of glaucoma? *Include a definition of primary and secondary glaucoma

A

Increased intraocular pressure

  • Primary: no underlying cause
  • Secondary: i.e from drugs or trauma
33
Q

What visual symptom is very typical of glaucoma?

A

Visual field loss - arcuate scotoma (arc-shaped blindspot)

*add photo in pro

34
Q

What is diabetic retinopathy and what causes it?

A

Due to prolonged hyperglycemia, HTN, cholesterol; blood vessels to the eye become chronically and progressively damaged and there is an attempt to form new microvasculature

35
Q

What is the most common cause of blindness in the UK ?65 years? Define this condition

A

ARMD: age related macular degeneration; changes occuring in the macular without an obvious cause and new vessels forming around the macula

36
Q

Name six risk factors for acquiring ARMD

A

> 60 years, female or men, smoking, HTN, BMI and genetics

37
Q

How is vision affected in ARMD?

A

Progressive loss of central vision

38
Q

Differentiate between dry and wet ARMD

A

Dry: retinal depigmentation and formation of drusen (small yellow or white spots on the retina). Tends to be slow and progressive

Wet: new blood vessels invade macular and leak, tends to be more rapid

39
Q

What is the focal length of a lens and what does it depend on?

A

The focal length is the distance from the lens to the point of focus and depends on the strength of the lens/the lens’ dioptric strength

40
Q

Define visual acuity. Where is it highest and why?

A

Our ability to distinguish the separateness of two sources of light/two-point discrimination
Highest in the fovea as there is less scattering of light

41
Q

What is the acuity and visual field of peripheral vision ?

A

Low acuity but wide visual field

42
Q

Describe how the optic nerve structurally links to the brain

A

Since its part of the CNS…
1. Its encased in a tube of CT that are continuations of the meninges of the brain

  1. Within the meninges of the optic nerve is CSF that is also continuous with the ventricular system of the brain
  2. Blood vessels within the optic nerve are also direct continuations of vessels of the brain
43
Q

What is the point of origin for the optic nerve within the retina?

A

The optic disc or ‘blind spot’

44
Q

What fills the anterior segment of the eye?

A

Aqueous runny/watery fluid

45
Q

Describe the three layers surrounding the eye

A
  1. Sclera
  2. Choroid layer: pigmented layer - has the blood vessels
  3. Retina: has nerve fibres from the optic nerve
46
Q

How would you correct for hypermetropia?

A

Putting in a convex lens so that the light rays converge and the image is formed on the retina (not behind it)

47
Q

How does the eye add to its dioptric strength and how is this done?

A

By increasing the convexity of the lens, this is done by the process of accommodation where the contraction of the ciliary muscles causes the lens to become more convex

48
Q

What is the near point? What is the normal value and what does this value depend on?

A

The shortest distance in front of the eye where an object can be maintained in focus

Normally ~25 cm and is dependent on age and the state of the eye (i.e for short sighted persons it will be closer to the eye than normal and for long sighted persons further away)

49
Q

What nerve is responsible for the thickening of the lens and constriction of the pupil in accommodation?

A

CN III parasympathetic fibres (is the efferent)

50
Q

Describe the pathway of the optic nerve to the brain

A

From the retina -> optic chiasma (inner fibres cross over) -> Optic tract -> lateral geniculate nucleus in the thalamus -> radiations -> primary visual cortex in occipital lobe

51
Q

Which fibres from each eye will you find crossing over in the optic chiasm - which fibres will you then find in the optic tract?

A

In the chiasma: The inner/nasal fibres

So in the tract there will be fibres from the same temporal side and the opposite nasal side

52
Q

What type of visual loss is experienced when there is a lesion to the optic tract? What is likely to cause this?

A

Homonymous hemianopsia - stroke

*add photo in pro

53
Q

What type of visual loss is a pituitary tumour likely to cause?

A

Bilateral hemianopsia (loss of the temporal/lateral vision on both eyes) - as it is located mid-chiasma and therefore affects the nasal/inner fibres from both eyes

54
Q

The maintenance of the axial length depends upon intraocular pressure. What is this pressure and how is it maintained?

A

Intraocular pressure is maintained at ~10-21 mmHg. In the aqueous humor (in the anterior segment) the osmotic cavity is above that in the blood, so fluid is drain into it from the ciliary body and possibly the iris. It escapes back to the venous system through the canal of Schlemm at 5-6 mL/day

55
Q

Name one condition which leads to a raised intraocular pressure, how does this affect the axial length of the eye?

A

Glaucoma; caused by an imbalance between the rate of secretion of the vitreous humor and its reabsorption. This distorts/lengthens the axial length of the eye

56
Q

What does it mean to add or subtract diopters? Which would you do for a long vs short sighted person?

A

Add diopters means use a convex lens, subtracting diopters means using a concave lens

Long sighted person: dioptric strength mused be increased and a convex lens used

Short sighted person: here the dioptric strength is too great for the eye’s axial length and must be subtracted by diverging the light rays with a concave lens

57
Q

How does the eye add to its dioptric strength and how is this done?

A

By increasing the convexity of the lens, this is done by the process of accommodation where the contraction of the ciliary muscles causes the lens to become more convex

58
Q

What is the near point? What is the normal value and what does this value depend on?

A

The shortest distance in front of the eye where an object can be maintained in focus

Normally ~25 cm and is dependent on age and the state of the eye (i.e for short sighted persons it will be closer to the eye than normal and for long sighted persons further away)

59
Q

As your visual system can compensate for your natural blind spot, are large “blind” areas in the visual field of a patient obvious to them?

A

No, very large areas of the visual field can be lost without the subject being aware - their loss is only apparent when the extent of the visual fields is measured

60
Q

What are pathological blind areas called?

A

Scotomata

61
Q

What is the commonest form of color blindness and which gender is it more common in?

A

Red/green, more common in males as it a sex-linked characteristic

Jess Nervous (16 decks)

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